1. Field of the Invention
The present invention is an invention which is useful, when applied to an information recording/reproducing method and device useful for recording encrypted information in an information recording medium, a method and device for reproducing information from an information recording medium in which encrypted information is recorded, an information recording medium in which encrypted information is recorded, and an information reproducing medium.
2. Description of the Related Art
In a case where information is recorded in an information recording medium such as an optical disc, the information is sometimes required to be encrypted and recorded. For example, in a copyright protection system, a content which is a writing is encrypted with an encryption key to form an encrypted content. Furthermore, the content is encrypted with another encryption key to form an encrypted encryption key in order to keep secret the encryption key used for encryption. The encrypted encryption key is recorded together with the encrypted content in the recording medium to prevent illegal copying.
At present, the following handling is performed in the copyright protection system concerning a digital versatile disc (DVD) which is rapidly expanding its market. That is, there is utilized a content scramble system (CSS) licensed by DVD Copy Control Association (DVD CCA) in a DVD video in which a video signal for exclusive use in reproduction is recorded. A content protection for prerecorded media (CPPM) system is utilized in a DVD audio for exclusive use in reproduction. A content protection for recordable media (CPRM) system is utilized in the copyright protection system of the content to be recorded in the recording medium. Licensing of the CPPM and CPRM systems is performed by specific organizations (e.g., organizations called 4C Entity and LLC).
On the other hand, there has further been advanced development of a high-capacity next-generation DVD or the like in which a high-definition video, a voice signal or the like is recordable/reproducible. There is a demand for introduction of a system in which a security ability is improved more than in a conventional technology in the copyright protection system in a case where a writing having a high quality level is recorded in the next-generation recording medium.
That is, in recent years, digital-TV broadcasting or the like has been started in which a high definition video (HD-Video) is broadcasted. A copyright holder side requires a security system which has been advanced more than in the conventional technology as recording permission conditions with respect to a recording/reproducing system to record/reproduce a broadcasted program. On the other hand, a user demands a freely usable system as long as a form of use is correct. If inconvenient use is enforced because of some illegal users, oppositions are to be expected.
In this situation, it is important to improve a function of a basic portion in a system which copes with the next generation. Basic requirements for content protection will be described below:
1) prevention of bit-by-bit copying;
2) encryption of the content;
3) system renewability; and
4) securement of perfectibility of copy control information (CCI).
In examples of the CPPM or the CPRM, the following handling is performed:
concerning 1), the bit-by-bit copying is prevented by adding of an inherent ID to each medium;
concerning 2), a cryptographic unit is sophisticated;
concerning 3), a media key block (MKB) is adopted; and
concerning 4), CCI is utilized (application-dependent) as the encryption key.
An encryption system is constituted using a structure in which characteristics or properties of individual constituting elements are skillfully utilized in this manner, and accordingly efforts are made to realize required specifications.
Concerning 1) . . . When the inherent ID added to each medium is utilized, the following functions can be obtained. In a case where the content is encrypted with the encryption key related to the inherent ID, even if the encrypted content is directly copied to another medium, decryption cannot be correctly performed, and the bit-by-bit copying can be prevented.
Concerning 2) . . . The encryption depends on an ability of the cryptographic unit, and the cryptographic unit having a high ability is being adopted. Moreover, an MKB is a set of device keys installed as secret keys in a device which records/reproduces the content with respect to the recording medium, and is a media key block in which a media key as a base key for content encryption is encrypted to arrange a mathematical system. When the device key of the recording/reproducing device is hacked to perform illegal utilization, a new MKB is newly issued. The new MKB is adopted in a newly issued recording medium. As a result, when the information of the newly issued recording medium is processed, calculation and generation are performed by a bunch of keys from which a hacked object (device key) has been removed. An illegal recording/reproducing device having the hacked device key cannot use the recording medium in which the new MKB is recorded. That is, the hacked recording/reproducing device is revoked from the copyright protection system. In this processing, a system renewability function works.
The CCI is a control flag for each content such as copy prohibition or copy-once, but tampering of the flag itself needs to be prevented. Therefore, the CCI is utilized as the encryption key to thereby complicate the tampering.
As described above, even at present, a sophisticated technology has been used with respect to enhancement of reliabilities of the constituting elements and improvement of the security ability by the system in order to cope with necessary protection requirements.